Precise measurement of variations in the local gravitational acceleration is valuable for natural hazard forecasting, prospecting, and geophysical studies. Common issues of the present gravimetry technologies include their high cost, high mass, and large volume, which can potentially be solved by micro-electromechanical-system (MEMS) technology. However, the reported MEMS gravimeter does not have a high sensitivity and a large dynamic range comparable with those of the present commercial gravimeters, lowering its practicability and ruling out worldwide deployment. In this paper, we introduce a more practical MEMS gravimeter that has a higher sensitivity of 8 μGal/√Hz and a larger dynamic range of 8000 mGal by using an advanced suspension design and a customized optical displacement transducer. The proposed MEMS gravimeter has performed the co-site earth tides measurement with a commercial superconducting gravimeter GWR iGrav with the results showing a correlation coefficient of 0.91.

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This paper presents a micromachined micro-g capacitive accelerometer with a silicon-based spring-mass sensing element. The displacement changes of the proof mass are sensed by an area-variation-based capacitive displacement transducer that is formed by the matching electrodes on both the movable proof mass die and the glass cover plate through the flip-chip packaging. In order to implement a high-performance accelerometer, several technologies are applied: the through-silicon-wafer-etching process is used to increase the weight of proof mass for lower thermal noise, connection beams are used to reduce the cross-sensitivity, and the periodic array area-variation capacitive displacement transducer is applied to increase the displacement-to-capacitance gain. The accelerometer prototype is fabricated and characterized, demonstrating a scale factor of 510 mV/g, a noise floor of 2 µg/Hz1/2 at 100 Hz, and a bias instability of 4 µg at an averaging time of 1 s. Experimental results suggest that the proposed MEMS capacitive accelerometer is promising to be used for inertial navigation, structural health monitoring, and tilt measurement applications.

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Capacitive micro accelerometers with high sensitivity have found wide applications in geophysics. Reducing the interelectrode spacing, which is determined by the thickness difference between the electrodes and the solder bumps in flip-chip eutectic bonding, is an efficient way to improve the sensitivity of area-varying capacitive transducers in micro accelerometers. Traditional methods require extra materials and processes, and precise control of the thickness of both the solder pumps and the electrodes is necessary. This work introduces a novel method for the precise control of the interelectrode spacing using a three dimensional (3D) electroplating process. Standoff pillars and electrodes are deposited by a single electroplating process with a constant thickness difference, which is only determined by the gap of the seed features that can be precisely determined by photolithography. The standoff pillars are used to define the thickness of the solder bumps in the packaging process. The 3D electroplating process is studied, characterized and applied to a typical high-precision micro capacitive area-varying accelerometer. Experimental results show that the variation of the interelectrode spacing is decreased by more than 6.5 times, when compared to that without the 3D electroplating process. Benefitting from the reduced interelectrode spacing, the sensitivity is increased by more than 3 times, while the resolution is 10 ng (√Hz)−1, which is 2.5 times better. It is believed that such a method can be applied to MEMS devices where interelectrode spacing needs to be precisely controlled.